Magnetic core elements for rotating electrical machines

ABSTRACT

Magnetic core elements for rotating electrical machines which are prepared by winding a magnetic steel strip several times while applying a sufficient pressure permanently to deform it into a flattened state so as to obtain a smooth surface on both sides of the resultant coil, spot welding the individual turns at least near the forward and rear ends of the coiled strip rigidly to form them into an integral body and punching a plurality of slots through which to insert the winding of a rotating electrical machine in a prescribed periphery of the coil.

United States Patent i191 Akiyamaet a1. i

1 1 a Jan. 2, 1973 54 MAGNETIC Conn ELEMENTS FOR ROTATING-ELECTRICALmoms [75] Inventors: Yujil Akiyama; Yasuyom, lshii; Shigeo 01mm" SaburoTakeshimn, all of Mie-ken,.Japan [73] Assignee: Tokyo Shibaurn ElectricCo., Ltd.,

Kawasaki-shi; Japan 22 Filed: Oct. 12,1971 211 App]. No.: 188,263

1,920,354 8/1933 Carpenter ..3 10/2 l 7 UX 2,845,555 7/l958Carpenteretal .Q. ..3l0/2l6 2,908965 10/1959 'Platt ...3 l0/l64 x3,436,812 4/1969 Aoki et al ..29/596 FOREIGN PATENTS 0R APPLICATIONS1,114,055 5/1968 Great Britain ..310 259 Primary Examiner-D. F. DugganAttorney-Solon B. Kemon et al.

[5 7] ABSTRACT Magnetic core elements for rotating electrical machineswhich are prepared by winding a magnetic steel strip several times whileapplying a sufficient pressure permanently to deform it into a flattenedstate so as to obtain a smooth surface on both sides of the resultantcoil, spot welding the individual turns at least near the forward andrear ends of the coiled strip rigidly to form them into an integral bodyand punching a plurality of slots through which to insert the winding ofa rotating electrical machine in a rws rihqlysr bqy the 1 Claim, 7Drawing Figures MAGNETIC CORE ELEMENTS FOR ROTATING ELECTRICAL MACHINESBACKGROUND OF THE INVENTION This invention relates to core elements forrotating electrical machines and more particularly to core elements forrotating electrical machines prepared by winding a magnetic steel stripseveral times while applying a sufficient pressure permanently to deformit into a flattened state and boring a periphery of the resultant coilwith a plurality of slots through which to insert the winding of therotating electrical machine.

A core element for rotating electrical machines is generally round andhas its periphery perforated with slots through which to insert thewinding of the electrical machine. A number of core elements are punchedout of a large magnetic steel sheet and the core is prepared bysuperposing these elements. Therefore, this punching unavoidably givesrise to considerable scraps, extremely reducing the rate of utilizingthe steel sheet. For example, where there is manufactured a core for afour-pole, 1.5 KW general purpose electrical motor, the steel sheet isonly utilized to an extent of 55 to 58 percent in punching coreelements.

To elevate the effective use of a steel sheet, there has been proposed amethod of preparing a core which consists in boring in advance the edgeof an originally manufactured narrow steel strip with a plurality ofslots through which to insert the winding of a rotating electricalmachine and winding the strip while applying a sufficient pressurepermanently to deform it into a flattened state until the resultantflattened turns are laminated to a desired extent in the direction ofthe thickness of the strip. However, each turn has a tendency to bebrought back to its original unwound state due to the residual stressresulting from the winding force to which it was initially subjected.With time, therefore, a core thus prepared becomes distorted. Further,the stress derived from the punching of the slots leads tovariation inthe outer and inner diameters of the coiled core, with the resultantfailure to effect the satisfactory alignment of the slots of thelaminated turns. Accordingly, the core according to the proposed methodpresents difficulties in being used with a rotating electrical machine,for example, an induction motor where there should be provided as closea clearance as possible between the stator and rotor, though it may beapplicable to a DC. or synchronizing rotating electrical machine wheresaid clearance has a relatively large latitude. Therefore, the aforesaidproposed core has not yet been put to practical application.

Another type of core proposed to date is formed by helically, winding asteel strip which is not previously bored with slots through which toinsert the winding of a rotating electrical machine while similarlyapplying a sufficient pressure permanently to deform it into a flattenedstate; cutting off each turn of the helical coil during said windingstep; and punching the slots in each cut off turn. This type of corepermits the easy alignment of the winding slots and the improvedroundness of its periphery, but still presents difficulties in beingused with a rotating electrical machine for example, an induction motorwhere there should be allowed as close a clearance as possible betweenthe stator and rotor.

The first mentioned core of the prior art has the drawback that a coreformed by winding a previously slotted steel strip presents a polygonalperiphery corresponding to the number of slots, formed, and moreover hasdifferent yield conditions between the slot bottom and the othernonslotted portions of the strip, presenting difficulties in aligningthe slots of one turn with these of another due to the deformationresulting from said different yield conditions.

SUMMARY OF THE INVENTION It is accordingly an object of this inventionto provide a magnetic core element which is prepared by winding a steelstrip several times while applying a sufficient pressure parmanently todeform it into a flattened state so as to obtain a smooth surface onboth sides of the resultant coil, jointly fixing the turns thereof atleast near the forward and rear ends of the coiled strip and punching aplurality of slots through which to insert the winding of a rotatingelectrical machine in a prescribed periphery of the coil.

Another object of the invention is to provide a method for manufacturingsaid coil elements.

Still another object of the invention is to provide an apparatus formanufacturing said coil elements.

A core element according to this invention is prepared by winding amagnetic steel strip several times so as to laminate the individualturns of the resultant coil in the direction of the thickness of thestrip. The forward and rear ends of the coiled strip face each otheracross an imarginary line parallel with the direction of the thicknessof the laminate. The intermediate section of a laminated strip is bentat two close points facing its forward and rear ends through the sameangle in opposite direction to an extent totally corresponding to thethickness of the strip itself so as to render the nonbent parts ofsaidintermediate section parallel with each other, thereby forming astepped portion. The forward and rear ends of the coiled strip aredisposed opposite to each other across said stepped portion. Thelaminated turns of the coil are spot welded at least near said forwardand rear ends rigidly to form them into an integral body so as to obtaina substantially smooth surface on both sides of the coil. A coil elementthus prepared is finally bored in a prescribed periphery with aplurality of slots through which to insert the winding of a rotatingelectrical machine.

A core having a sufficient thickness for actual use with a rotatingelectrical machine is constructed by further superposing a proper numberof the aforementioned core elements with the slots thereof accuratelyaligned. In said superposition it is preferred that the aforesaidstepped portion defined between the forward and rear ends of a coiledstrip constituting each core element be not arranged on the same lineparallel with the direction in which there are superposed said coreelements.

The preferred method of manufacturing core elements comprises the stepof winding a magnetic steel strip so as to be laminated in the directionof the thickness of the strip. During this step, the steel strip issubjected to a desired permanent deformation to facilitate the executionof the succeeding steps.

The laminated steel strip is drawn out in a helical fonn, starting withits forward end. That portion of the wound strip which represents adesired number of turns is cut off to form a unit coil. The coil issubjected on both sides to a sufficient lateral pressure to bepermanently deformed into a flattened state with the inner and outerdiameter of V the coil maintained at a prescribed value. Upon completionof said permanent deformation, the turns of the coil are welded togetherinto an integral body at least near the forward and rear ends of thecoiled strip with the lateral pressure still applied. The flattened coilconsisting of said welded turns is perforated in a prescribed peripherywith a plurality of slots through which to insert the winding of arotating electrical machine.

A unit magnetic core element thus prepared is prominently improved indimensional precision and well adapted for use with a rotatingelectrical machine where there should be provided as close a clearanceas possible between the stator and rotor.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of a unit coreelement according to an embodiment of this invention;

FIG. 2 is a perspective view of a helical coil or unit core elementprepared by cutting off that portion of the wound steel strip whichrepresents a prescribed number of turns;

FIG. 3 is a side view of the core element where the helical coil of FIG.2 is compressed with a lateral pressure to have its turns flattened;

FIG. 4 is a side view of the core element where it is subjected to afurther lateral pressure to have both sides permanently deformed into asmooth surface;

FIG. 5 is a side view of the core element where its flattened turns arewelded together in several places;

FIG. 6 is a plan view of the core element of FIG. 5; and

FIG. 7 is a schematic side view, partly in section, of an apparatus forcontinuously manufacturing the core element of FIG. 5 from a magneticsteel strip.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, numeral 1represents a unit core element according to this invention which isprepared by winding, for example, twice a steel strip 2 of prescribedwidth to be laminated in the direction of its thickness so as to form aunit coil element, its outer and inner peripheries being indicated bynumerals 3 and 4 respectively. The inner periphery 4 is perforated witha plurality of slots 5 through which to insert the winding of a rotatingelectrical machine. As shown in FIG. 5, the forward and rear ends 60 and6b of the coiled strip 2 closely face each other across an imarginaryline parallel with the direction in which the turns of the coil arelaminated. The intermediate section of the laminated strip 2 is bent attwo close points facing its forward and rear ends 60 and 6b through thesame angle in opposite directions to an extent totally corresponding tothe thickness of the strip itself so as to render the nonbent parts ofsaid intermediate section parallel with each other, thereby forming astepped portion 8 between said forward and rear ends 6a and 6b. Aspreviously mentioned, the coil 1 is subjected to a sufficient lateralpressure to have its turns permanently deformed into a flattened stateso as to obtain a smooth surface on both sides of said coil 1. The turnsare spot welded into an integral body at two points 9a and 9b near theforward and rear ends 6a and 6b of the coiled steel strip 2 respectivelyand at another I point 9c preferably disposed opposite to the firstmentioned points 9a and 9b. Upon completion of said spot welding, theslots 5 are press punched. The number of turns constituting the unitcore element 1 is not limited to two turns, so long as the perforationof the slots 5 is not obstructed. A desired number of unit core elements1 are further superposed with the slots accurately aligned finally toprovide a stator core for a rotating electrical machine. If the outerperiphery 3 of the unit core element 1 is bored with the slots 5, theresultant core will be adapted for use with a rotor. In either case, itis preferred that said superposition of the core elements 1 be effectedwith the stepped portion 8 defined between the forward and rear ends ofthe laminated strip of the respective core members 1 properly displacedfrom one another in a lengthwise direction.

The unit core element 1 may be manufactured with an apparatusillustrated in FIG. 7 and through the steps described by reference toFIGS. 2 and 6. Referring to FIG. 7, numeral 11 represents a shaftconnected to a source of drive power so as to rotate clockwise as viewedin the direction of the arrow. To the forward end of the shaft 11 isconnected through a joint 12 the later described rotating mandrel 13whose diameter is designed to define the inner diameter of the coilelement 1. A steel strip 14 is supplied to the rotating man drel 13 tobe wound about it in a closely laminated form so as to form a coil 15.Around the periphery of the rotating mandrel 13 are concentricallydisposed a plurality of rollers 16 rotating in the direction in whichthe steel strip 14 is wound about the mandrel 13 so as to apply pressureto the periphery of the coil 15. There is further provided apressurizing plate 17 which rotates while pressing the side of the steelstrip 14 against the side of the coil 15 so as to help the strip 14 tobe properly wound about the mandrel 13. In addition, there are provideda plurality of lateral pressure rollers 18 so as to press said pressureplate 17 against the coil 15. There are further provided guide membersand 19b for successively drawing out the coil 15 in a helical form,starting with its forward end. There are used other guide members 22a,22b and 220 for feeding the helical coil thus drawn out to anothermandrel 20 with a prescribed pitch allowed between the adjacent turns.The latter guide members 22a, 22b and 220 are per.- forated with slots23 to define said pitch. There are also provided a limit switch 24 fordetecting the forward end 6a of the helical coil and a cutter 25 forcutting off upon receipt of a detection signal from the limit switch 24that portion of the helical coil which represents a required number ofturns for a unit helical coil.

The second mandrel 20 is disposed concentrally with the first mandrel13, the lengthwise central portion of which has a diameter for definingthe inner diameter'of the helical coil, said diameter beingprogressively reduced toward both ends of said mandrel 20.Concentrically with the mandrel 20 is disposed a guide cylinder 26 whoseinner diameter is designed to limit the outer diameter of the unit coreelement 1 of FIG. 1. Said guide cylinder 26 has a plurality oflengthwise slits bored in the outer wall. At that part of each slit 27which faces the maximum diameter of the mandrel is disposed a stopper soas to cross the slit in the peripheral direction of the guide cylinder26. There are provided a plurality of rotating pressurizing members 32,each of which is pivoted about a fixed shaft 29 so as to oscillate inthe direction of the arrows 30 through that part of the slit 27 which isdisposed on the indicated right side of the stopper 28. The clockwiserotation of the pressurizing member 32 is limited by the stopper 28. Thepressurizing member 32 has an arcuate guide hole 33 perforated insidethe periphery. An arcuate electrode 34 is made to travel through saidarcuate guide hole 33 in a state insulated from the pressurizing member32 by means of a pressurizing plate 35 and an elastic member 36. Thereis provided a tightening member 38 which is made to move in thedirections of the arrows 37 through that part of the slit 27 which ispositioned on the indicated left side of the stopper 28.

Now for convenience, each cut off helical coil consisting of a desirednumber of turns is designated as a (FIG. 2), a coil obtained simply bycompressing the coil 40a is indicated as 40b (FIG. 3), a coil obtainedby applying a lateral pressure to the coil 40b permanently to deform itinto a flattened state so as to provide a smooth surface on both sidesis denoted as 400 (FIG. 4), and a coil derived from the spot welding ofthe turns of the coil 400 at several points in referred to as 40d.Referring to FIG. 7, the aforesaid rotaing pressurizing member 32 andtightening member 38 are so positioned as to spot weld the turns of thecoil 400 while said coil 400 is subjected to a lateral pressure forpermanent deformation. Between the arcuate electrode 34 and thetightening member 38 is disposed a source of welding power (not shown).However, said spot welding may be effected by utilizing the rotatingpressurizing member 32 as one electrode and the arcuate electrode 34 asthe other.

The unit core element 1 is manufactured by the undermentioned series ofsteps. The steel strip 14 continuously fed to the apparatus is closelywound into the coil 15 having the prescribed inner and outer diameterswhile being permanently deformed by the movement of the rotating mandrel13, peripheral pressure rollers 16 thehelical coil is brought to theposition of the limit switch 24, that portion of the helical coil whichrepresent a required number of turns for a unit coil is cut off by thecutter 25, obtaining a unit coil element 40a. The number of turns to becut off each time may be freely chosen. At a prescribed point of time,the operating surface of the rotating pressurizing member 32 is broughtinto an annular space defined by the peripheral surface of the mandrel20 with the inner wall of the guide cylinder 26. The cut off helicalcoil 40a is conducted to the operating surface of the rotaingpressurizing member 32 along the periphery of the mandrel 20 by aelectromagnetic device or feed means using compressed air (not shown).The tightening member 38 is urged from a position marked by the dottedlines to that defined by the solid lines illustrated in HO. 7 to pressthe helical coil 40a against the operating surface of the pressurizingmember 32. Smce said pressurizing member 32 is driven clockwise, thehelical coil 40a is permanently deformed under pressure into the coil400 through the form 40b of FIG. 3. While this pressure is applied, thearcuate electrode 34 rotates clockwise by means of the pressurizingplate 35 to spot weld the turns of the coil 40c at the aforesaidprescribed points 9a, 9b and 9c. Upon completion of spot welding, thepressurizing member 32 and the tightening member 38 are brought back totheir original positions and there is taken out the coil 40d spot weldedat the points 9a, 9b and 9c shown in FIG. 5. The coil 40d is perforatedwith slots by the known punching means.

This invention is not limited to the aforementioned embodiment, butincludes any other modification which does not depart from the scope andobject set forth in the claims.

What we claim is:

1. Magnetic core elements for rotating electrical machines consisting ofa coil of several turns formed by winding a magnetic steel strip in alaminated form in the direction of the thickness of said strip;comprising a peripheral portion with a plurality of slots to insertwindings of said rotating electrical'machine, forward and rear ends ofsaid coiled strip facing each other across an imaginary line parallelwith the direction in which said turns of said coil are laminated, anintermediate stepped portion having a depth equal to the thickness ofsaid strip itself and two bent portions at said forward and rear ends,said stepped portion oppositely facing said forward and rear ends,thereby obtaining a smooth surface in both sides of said coil, andwelded portions which join said turns at at least two points near saidforward and rear ends of said coiled strip.

1. Magnetic core elements for rotating electrical machines consisting ofa coil of several turns formed by winding a magnetic steel strip in alaminated form in the direction of the thickness of said strip;comprising a peripheral portion with a plurality of slots to insertwindings of said rotating electrical machine, forward and rear ends ofsaid coiled strip facing each other across an imaginary line parallelwith the direction in which said turns of said coil are laminated, anintermediate stepped portion having a depth equal to the thickness ofsaid strip itself and two bent portions at said forward and rear ends,said Stepped portion oppositely facing said forward and rear ends,thereby obtaining a smooth surface in both sides of said coil, andwelded portions which join said turns at at least two points near saidforward and rear ends of said coiled strip.